This invention relates generally to image processing and more particularly to a pulsed illumination signal modulation control and adjustment method and system.
During the scanning of photographic images from film, various factors may affect the quality of the resulting digital image. For example, systems used to derive digital images from film may suffer from both sensor and illumination non-uniformities, each of which may adversely effect the signal integrity of the images. Image quality may also depend, in part, on the characteristics of the film. Where digital image data is obtained from developing film, the characteristics of the developing chemical applied to the film may also affect image quality.
For example, processing images from film typically includes capturing digital data from the film with a sensor as the film is illuminated with a light source. Because the illumination levels captured by the sensor represent the image data, any sensor or illumination non-uniformities introduce undesirable errors into the data measurements. Unfortunately, sensor and illumination characteristics typically vary individually and can drift over time due to factors such as heating and/or transient responses in the devices when they are activated and deactivated. Where the film is scanned while being developed, variances in film and chemical developer characteristics often arise due to changes that take place during the development process. Signal levels captured by the sensors may also vary due to factors such as aging of the sensors or light sources.
In addition, some systems may produce inaccurate data due to noise that is introduced by variances in illuminated power as a light source operates. For example, a light source may emit one pulse of illumination, during which a sensor may capture data. Any differences in illuminated power between pulses are captured by the sensor, including sensor or illumination characteristics that change during the development process. These differences may be erroneously interpreted as differences in data content captured from the film.
From the foregoing, it may be appreciated that a need has arisen for providing a pulsed illumination signal modulation control and adjustment method and system. The present invention substantially reduces or eliminates disadvantages and problems of existing systems.
One aspect of the invention is a method for signal modulation adjustment. The method comprises illuminating a reference target and a region of film with a first light source for a first time interval. The method further comprises capturing image data from the film in response to a first amount of light reflected from the film with a first sensor for a first integration time. The method also comprises approximately simultaneously producing a first reference output in response to a first amount of light reflected from the reference target in a field of view of a reference sensor. More particularly, the method further comprises adjusting the data in response to the reference output. In a further embodiment, the method comprises adjusting an output illumination level of the first light source in response to the first reference output before a next time interval.
The invention provides several important advantages. Various embodiments of the invention may have none, some, or all of these advantages. The invention may improve the accuracy of image data. For example, the invention may compensate for drift or other variations in sensor or illumination source characteristics between image capture sampling times. The invention may automatically adjust illumination levels and/or sensor integration time using a reference or sensing detector. Signal modulation can be stabilized between illumination pulses, to reduce signal noise. The invention may also prevent saturation of sensors in varying film, developer, and illumination conditions.
Alternatively or in addition, the invention may adjust the captured image data to compensate for such variations. For example, sensor and illumination non-uniformities in the image data may be normalized and various gains for the image data may be adjusted using the measured data. Other technical advantages may be readily ascertainable by those skilled in the art from the following figures, description, and claims.